Green-Solvent-Processable, Dopant-Free Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells
Nobuko Onozawa-Komatsuzaki a, Daisuke Tsuchiya b, Shinichi Inoue b, Atsushi Kogo a, Takurou N. Murakami a
a National Institute of Advanced Industrial Science and Technology (AIST)
b Nippon Fine Chemical Co., Ltd.
Poster, Nobuko Onozawa-Komatsuzaki, 066
Publication date: 24th October 2023

The hole transporting material (HTM) is among the most important components of perovskite solar cells (PSCs) because it plays a crucial role in achieving high performance by allowing for charge recombination reduction. At present, 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD), a wide-band-gap material, is the most frequently used HTM, and devices based on spiro-OMeTAD exhibit excellent performance. However, pristine spiro-OMeTAD films exhibit low conductivity and mobility. To overcome this limitation, dopants such as lithium bis(trifluoromethylsulfonyl)imide [Li(TFSI)], 4-tert-butyl-pyridine (TBP), and FK209 have been used for developing PSCs with high power-conversion efficiency (PCE). Despite the enhanced hole transport properties, the doping strategy causes several problems. For example, commonly used dopants, such as Li(TFSI) and TBP, have a hygroscopic or volatile nature, which leads to accelerated degradation of PSCs. These instability problems must be overcome for the commercialization of PSCs [1, 2].

Recently, dopant-free HTMs have been largely explored to improve the performance and stability of PSCs, and significant progresses have been made [3]. On the other hand, in current reports, halogenated solvents (e.g., chlorobenzene and chloroform) are commonly used for HTMs in PSCs since there are very few solvents for HTMs in PSCs that do not damage the perovskite layer; however, their use should be avoided as they are known to be hazardous to the environment. Herein, we synthesized a nonhalogenated-solvent-soluble, dopant-free HTM, SF62 [4]. When depositing HTMs for PSCs, SF62 could be dissolved with a nonhalogenated and green solvent, ethyl acetate (AcOEt). It is one of the most common organic solvents and is known to have a low environmental impact. Non-doped-SF62-based PSCs exhibited higher PCE (18.6%) than doped spiro-OMeTAD-based ones (18.3%), with enhanced stability.

Stability test of this research was partly supported by the New Energy and Industrial Technology Development Organization (NEDO, JPNP21016).

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